The present teachings relate to methods for controlling insect pests.
Fire ants are known as pests across the globe and comprise almost 300 different known species of stinging ants. Most fire ant species are not a serious threat to humans and of the few species that are, most are controlled by natural forces such as parasites, predators and natural competition from other ant species. The species known as the red imported fire ant (Solenopsis invicta, also referred to as “RIFA”) originated in South America and was inadvertently imported into the southern United States in 1929. Since then, in the absence of its natural predators, parasites and competitors, S. invicta has spread from coastal areas of Alabama to infest large parts of the southern U.S. Farmers and homeowners consider them a serious pest, and more recently they have spread to parts of Asia and Australia.
Fire ants feed primarily on young plants and germinating seeds and can cause significant agricultural damage, particularly to grain, fruit, nut and root crops. They occasionally eat other insects such as crickets, and may attack small animals and can kill them. They nest in soil and their large mounding nests have been linked to the decline of ground nesting birds such as the Bobwhite Quail. Although typically not a serious health threat, the sting of the fire ant can be quite painful and the discomfort is multiplied when, as often happens, the victim is attacked by multiple ants and suffers repeated stings. Sting sites are at risk of infection and scarring. Anaphylaxis is a known risk for certain individuals with heightened immunologic sensitivity to fire ant venom.
Individual mound treatment and broadcast treatment are two approaches to fire ant control using insecticides such as carbaryl, diazinon, and dursban, or an insect growth regulator. Both methods are limited primarily by the requirement that the active compound make direct and sometimes lasting contact with the colony ants and particularly the queen. Individual mound treatment is limited by the fact that the queen is sometimes too deep within the colony to be contacted by the active compound. Care must be taken not to disturb the mound prior to application of the drench. A disturbance will alert the colony and the queen may be taken deeper into the mound. In addition, application of insecticidal surface dusts or granules have a limited effect on a colony if they are not watered in. Dissolved granules must come into direct contact with the ants to have any effect. As in mound drenches, care must be taken not to disturb the colony prior to application. Some insecticides are intended as injectants. While injectants can be more effective than surface applications or mound drenches, they are also more expensive and can be dangerous if not handled properly.
Certain biological control methods have been tried. In the southern United States a species of phorid flies, a natural parasite of fire ants, have been introduced. Not all introductions have been successful, although the fly has been established successfully in some sites in every southeastern state. In Australia, fire ant colonies have been controlled with ground bait of food laced with contraceptive compounds that make the queens infertile. Some success has been obtained at the cost of instituting a necessarily highly organized, lengthy and costly national eradication campaign, including acquisition and analysis of satellite imaging data at a huge and ongoing financial cost. Moreover, broadcasting baits are limited by a slow time course of action, lack of specificity to fire ants, influence of temperature on ant retrieval of the bait, and the fact that the baits dissolve in water and become irretrievable by fire ants. A need thus remains for inexpensive, easy to use and effective methods for controlling fire ant infestations.